1. Field of the Invention
The present invention relates to an exposure apparatus using a charged particle beam such as an electron beam. In particular, it relates to an electron gun for generating the electron beam used for drawing predetermined patterns on a material to be exposed (particularly, a wafer) in an electron beam exposure apparatus.
2. Description of the Related Art
Conventionally, there are many known electron beam exposure apparatuses, for example, a variable rectangular exposure apparatus, a block exposure apparatus, and a blanking aperture array (BAA) exposure apparatus. In these exposure apparatuses, there is a mask or block mask having a rectangular aperture in order to form a cross-sectional shape of the electron beam, art aperture having an optional shape used as a unit of repeating figure, and a plurality of apertures arranged in matrix. The electron beam is formed by irradiating a desired area of the aperture on the mask so that a desired pattern is drawn on the wafer.
In this case, the uniformity of the electron beam irradiated to the wafer has a large influence to a line width of the pattern to be drawn. For example, when it is assumed that an allowable line width is 0.01 .mu.m when drawing a line having a width of 0.1 .mu.m, the uniformity of beam irradiation is allowed for fluctuation of only a few percent. As a result, an irradiation area which appears to be uniform becomes narrow, and an exposure area is reduced so that the throughput of the electron beam exposure apparatus deteriorates.